In the directions there is a picture of a very simple and elegant looking vent on p. 40. I believe the vent arch is a single 9in brick, vented with two parallel thin arches that leave a cavity about 1/3 to 1/2 the length of the brick, so 3" to 4.5" wide.

I'm building a small oven, 36". May I safely presume that such a vent is definitely wide enough to pull air as needed? The "pull" is not merely a function of area, but rather of "squareness" (a long slender vent really won't flow as nicely as a squarer vent of the same area).

Is the design shown there definitely sufficient or should I make the vent wider than shown in that picture?

I read that it is wise to keep the area of the vent larger than the area of the flue. I'm using an 8 inch Duravent pipe which has 50 square inches. So, I plan to keep the vent area larger than that. Around 4.5 x 14 is where I expect to end up from an 18 inch opening; which is 63 square inches.

I have a 36" Pompeii, my vent opening is 14" x 7", and my chimney is 6". If I were to make my oven again I would consider a slightly larger vent. My vent works fine now, but when there is any wind I do loose some smoke out the front.

My vent is 20" x 6.5" that narrows down to about 7" x 6.5" with a 24" x 6" duratech chimney on top of that. While cooking, it draws just fine, but it is easy to overwhelm it during firing and get smoke out the front. I think the biggest drag in my whole setup might be the chimney cap. My chimney is just set in place and the vent draws smoke a lot better if I take the chimney off. An 8" chimney probably would have worked better.

I used the same image to design my vent.
( two thin arches across single firebrick width) resulting a a very thin narrow vent.

If I do it again, my vent will be the width of the entry! Front to back, at least 5 inches. Then I would probably narrow it up to a 13"x9" chimney flue. ( which is really 11x6.5" inside dimensions) Let's see, that would be about 100sq.in. down to 72 sq.in.

The main thing being the width, so that smoke has nothing impeding its upward flow.

Interesting, so width is actually more important so that the "sheet" of smoke exiting the entry arch turns right up into the vent without having its edges clipped. Perhaps the depth (front to back) of the vent is not as crucial as I originally thought.

On a similar point, I have been designing a full hemispherical entry arch instead of the far more common incomplete arch segment soldiered by a vertical sides, but that means my arch to dome transition doesn't have as flat a ceiling as the flatter incomplete arch designs. Will this also clip the smoke and trap it inside the oven?

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